I happened onto an article on the web by a gay designer who did the design for the Christie's auction of Marilyn Monroe's clothes in 2000, and was surprised by this passage. I think you will be too:
The process of cataloguing and displaying Marilyn’s bits took months. During this time I learned some crazily illuminating stuff about the breathy blond bombshell. Brace yourself for some next-level revelations.
Right away, I discovered that Marilyn was shockingly and unimaginably slender. She was sort of like Kate Moss but fleshier on top. Didn’t see that coming, did you?
When it came to finding mannequins to fit her dresses, I simply couldn’t. M.M.’s drag was too small for the average window dummy....
When you look at Marilyn on-screen and—armed with the information I have just provided—you realize that the busty, ample gal brimming over Tony Curtis in Some Like It Hot is literally one-third your size, you have every right to become suicidal. If she looks like that—zaftig, almost chubby—what on earth would you look like under similar circumstances?
Conventional wisdom says that the camera adds five pounds. After my Marilyn experience, I would say it’s more like 500 pounds.